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Homework Help: Thermal expansion?

  1. Sep 17, 2004 #1


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    thermal expansion???

    I need help asap!! the question goes like this...

    A cubic metal ox with sides of length 20cm contains air at pressure of 1 atm and a temperature of 300K. the box is sealed so that the volume is constant and heated to 400K. what is the net force on each side of the box? :confused:
  2. jcsd
  3. Sep 17, 2004 #2
    PV = nRT --> P/T = nR/V = const.
    P0= 1 atm T0=300k
    P1= P0*T1/T0 = 4/3 atm = 135100 Pa
    F= (P1 - Patm)* S = (135100 Pa - 101325 Pa)* (0.2m^2 * 6) = 8106 N

    Bye Final
  4. Sep 18, 2004 #3

    Doc Al

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    Staff: Mentor

    Well, I presume the net force on each side is zero! :smile:

    But I suppose they want you to find the outward force on each side of the box due to the pressure of the enclosed air.

    If you can assume that this box is itself in air at atmospheric pressure, then you can find the net force due to air pressure by subtracting the outside air pressure, like Final did.
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